Imaging apparatuses such as digital still cameras and digital video cameras capable of converting an optical image of the subject to an electrical image signal and outputting the image signal (hereinafter simply referred to as “digital cameras”) are rapidly becoming widespread. With reductions in size and weight and escalation in the magnification of optical zooming in recent years in particular, digital cameras have become significantly convenient for photographers (users).
Furthermore, lens-replaceable digital single-lens reflex cameras are rapidly becoming widespread in recent years. When the photographer sees the subject through a finder, this digital single-lens reflex camera causes light incident upon the photographing lens (that is, the image of the subject) to be reflected by a reflecting mirror placed on the photographing optical path after the lens, to change the optical path, converts the image of the subject image to an erect image through a pentaprism and so on, and guides the image of the subject to an optical finder. This allows the photographer to see the subject image through the lens from the optical finder. Therefore, the position where the finder optical path is formed normally is the regular position of the reflecting mirror.
On the other hand, if the lens is used to take photographs, the reflecting mirror immediately changes its position and is retracted from the photographing optical path, thereby switching the finder optical path to the photographing optical path. When photographs have been taken, the reflecting mirror immediately returns to the regular position. This scheme is common to a conventional film camera and a digital camera which adopt a single-lens reflex scheme.
One feature of a digital camera is that it is possible to photograph a subject by looking at the display apparatus (e.g. liquid crystal monitor) when a photograph is taken and check the photographed image immediately after taking a photograph. However, using the existing reflecting mirror scheme of digital single-lens reflex cameras entails a problem that the liquid crystal monitor cannot be used when a photograph is taken. Therefore, with an existing digital single-lens reflex camera, it is not possible to take a photograph using the liquid crystal monitor by looking into the finder and this is very inconvenient to a beginner who is unfamiliar with taking photographs using a digital camera in particular. Therefore, as shown in Patent Document 1, there is a demand for a function to allow the user to take a photograph using a liquid crystal monitor also when taking a photograph.
However, accompanying reductions in size and weight of not only digital single-lens reflex cameras but also digital cameras and escalation in the magnification of optical zooming, especially when a beginner uses a digital camera, a “blur” may occur in photographed images and may cause image quality degradation.
Patent Document 2 discloses a digital camera with a blur correcting optical system capable of reducing the influence on an image even when camera shake (which will be described later) occurs when a photograph is taken. The digital camera described in Patent Document 2 moves the correction lens up, down, left and right in directions perpendicular to the optical axis, depending on image shake of when a photograph is taken, and corrects image distortion. By this means, it is possible to take a photograph with reduced image shake using a smaller-sized and lighter-weighted digital camera. Furthermore, the digital camera disclosed in Patent Document 2 does not have to use a flash to emit light upon taking a photograph to prevent image shake, so that it is possible to take a photograph under conditions producing similar atmosphere to natural colors.
On the other hand, possible causes of image quality degradation of photographed images include “subject shake” caused by the motion of the subject, in addition to “camera shake” caused by vibration added to the camera by a shaking hand. Subject shake can be prevented by making exposure time shorter and taking a photograph at a high shutter speed. Shutter speed can be made faster by, for example, increasing photographing sensitivity or by using a flash light. As for optical image shake of the subject in the imaging plane, shake caused by vibration applied to the camera, will be referred to as “camera shake” and shake caused by the motion of the subject will be referred to as “subject shake” and camera shake and subject shake will be collectively referred to as “image shake with respect to the imaging plane.”
Patent Document 3 discloses a photographing apparatus with a motion prediction means for predicting the motion of the subject and changing photographing conditions such as shutter speed when the subject is likely to move, and a method applicable with the apparatus.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-125173    Patent Document 2: Japanese Patent Application Laid-Open No. 2000-13671    Patent Document 3: Japanese Patent Application Laid-Open No. 2006-157428